You have to make a contact to the persons you want to chat with. Then make an appointment with him/her!
I have made an appointment, but he/she never seems to come online. Whats wrong?
Did you remember the time difference from your local time to the time of your partner? This can be quite a few hours :-)
Find more info on http://www.timeanddate.com/worldclock/ for example.
How do I find out who is online for a chat?